1. Field of the Invention
The present invention relates generally to use of stent-grafts, and more particularly to devices used for fenestration of a stent-graft in situ.
2. Description of Related Art
A conventional main (vessel) stent-graft typically includes a radially expandable reinforcement structure, formed from a plurality of annular stent rings, and a cylindrically shaped layer of graft material, sometimes called graft cloth, defining a lumen, to which the stent rings are coupled. The stent rings includes straight portions that are referred to as struts. Main stent-grafts are well known for use in tubular shaped human vessels.
To illustrate, endovascular aneurysmal exclusion is a method of using a main stent-graft to exclude pressurized fluid flow from the interior of an aneurysm. This reduces the risk of rupture of the aneurysm and the associated risk of mortality.
Main stent-grafts with custom side openings are sometimes fabricated to accommodate particular vessel geometries of each individual patient. Specifically, as the location of branch vessels emanating from a main vessel, e.g., having the aneurysm, varies from patient to patient, main stent-grafts to treat such configurations are fabricated with side openings customized to match the position of the branch vessels of the particular patient. However, custom fabrication of main stent-grafts is relatively expensive and time consuming.
To avoid custom fabrication of main stent-grafts, side openings in the main stent-graft may be formed in situ. Illustratively, the main stent-graft is placed in the main vessel, e.g., the aorta, to exclude an aneurysm. Fenestrations may be made in situ to correspond to positions of the adjacent branch vessels. See U.S. Pat. No. 5,617,878 of Taheri.
The graft material of the main stent-graft is pierced with a needle at the ostium of a branch vessel, e.g., the renal artery, emanating from the main vessel. A fenestration is typically initiated with a small needle perforation of the graft material. The perforation must be enlarged with a conical dilator. However considerable force is required to push the dilator through the graft material and the use of such considerable force is difficult to control and can cause the graft material to deflect and move and/or suddenly tear causing the unexpected dilator motion which can damage or pierce the vessel wall opposite the dilator, which is not desirable.
Once the dilator opening has been made an expandable balloon is inserted in the opening in the graft material of the main stent-graft and the balloon inflated to tear or cut the graft material further.
If a small RF electrode, rather than a dilator is used to create the initial opening for the balloon, the initial application of force is reduced, however in both instances the use of the balloon cause tearing and fraying of the graft material. The use of a balloon to enlarge a graft opening is difficult to control and thus leads to unpredictability in the tear of the graft material or other complications. Further, the branch stent-graft tends to propagate the rent (a split or tear) in the graft material over time. Also, the edge of the rent fractured the branch stent-graft depending upon the particular application. Finally, the edge of the rent was a fray of loose fibers of the graft material, which tended to unwind over time.